It is known that mobile communications networks are constructed in cells for the widest possible coverage. A mobile communications cell is usually formed by a base station to which mobile communications antennas are typically fixed.
By means of these antennas of the base station, a corresponding cell is “illuminated”. As a consequence, a subscriber which is located within this mobile communications cell, and is typically mobile, can conduct communication with the base station and can have conversations with other subscribers in other mobile networks or in landline networks, for example.
The communication between the base station and mobile communications devices in a mobile communications cell is carried out using radio waves—as is known. As a mobile communications device increasingly approaches the cell boundary of a mobile communications cell, it requires increasingly greater energy to communicate with the base station. In other words, the mobile phone must now transmit more “loudly”—that is, increase its signal level—in order to be “heard”.
As the mobile communications device approaches closer to a base station, the required transmission power—the signal level—is regulated downwards. The mobile phone communicates increasingly more “quietly” with the base station.
The manner in which the communication between the base station and the mobile communications device works is specified by a number of regulations. These regulations specify maximum transmission strengths (signal levels), as well as minimum transmission strengths—generally depending on the given technology. According to the mobile communications standard (GSM, UMTS, LTE), there are different values for maximum/minimum signal levels.
The manner in which the transmission power of a mobile communications device is modified and/or regulated is found, by way of example, in the publication “WCDMA FOR UMTS”, third edition, Harri Holma and Antti Toskala, WILEY; (publication date: March 2016 (reprinted); general technical background). For example, page 55 and page 56, in the chapter “Power Control” state that whenever the mobile communications device in a mobile communications cell transmits with too strong a signal, the base station instructs the mobile communications device to lower the transmission power. If the transmission power of the mobile communications device is too low, the mobile communications station instructs the mobile communications device to increase its transmission power again. A corresponding measurement and instruction cycle is performed 1500 times per second, for example.
A known, fundamental problem arises in this context. The mobile communications devices (controlled by the base station) must be controlled at different distances from the base station in such a manner that the signal strengths at the base station are comparably high, such that no mobile communications device can “drown out” another—in other words, such that reliable communication can accordingly be carried out between a base station and all mobile communications devices in a cell.
If the mobile communications device is used in a motor vehicle, for example—rather than outdoors—it is generally advisable for a motor vehicle antenna mounted outside the motor vehicle to be used in order to handle the communication with a base station.
However, this requires the use of a corresponding coupling and line structure via which the transmission signals can be transmitted from the phone to the vehicle antenna—and vice versa when signals are received. However, the use of such a coupling and line structure ultimately causes an additional attenuation, which is why corresponding transmission signals not emitted by the mobile communications device itself, but via the motor vehicle antenna, would have a lower transmission power (lower transmission level).
In light of this context, the practice of inserting corresponding amplifier circuits which serve to compensate for the attenuation of the signal strength is known.
In this case, it is generally desirable for the amplifier (signal booster) to equalise or compensate for the existing additional attenuation (which is why these amplifiers are also sometimes called compensators) such that the communications between the motor vehicle exterior antenna and the base station can be conducted in exactly the same way as if the mobile communications device were used outdoors, outside of a motor vehicle, within a mobile communications cell without such an amplifier.
The aim of such an amplifying apparatus, and an associated control thereof, is to compensate for the additional attenuation caused by the coupling and line structure—which results in the reduction of transmission power.
Ideally, the amplifying apparatus would compensate for this attenuation in such a way that the transmission power at the motor vehicle antenna would be exactly the value at which a mobile communications device outdoors would communicate with a base station without such an amplifier.
In other words, therefore, the compensation is ideal and thus optimal with respect to signal attenuation in the transmission of transmission signals of a mobile communications device if the amplifying apparatus—that is, the circuit arrangement for compensating for signal attenuation—transmits in an identical manner to the transmitting power at which a mobile communications device would transmit when outdoors, for all transmissions of the transmission signals of a mobile communications device under the greatest possible range of operating conditions and especially under critical operating conditions, at a great distance as well as at a short distance from the base station. The specified values for the maximum and minimum signal level may not be exceeded. Also, it must be ensured that these values are reached.
In this context, DE 10 2013 101 590 A1 has suggested using at least one amplifier to compensate for an attenuation occurring on a signal path between a mobile terminal and an antenna, via which transmission signals originating in the mobile communications device can be amplified or attenuated. For this purpose, the circuit arrangement comprises a detection unit for detecting an input signal level from the mobile communications device, and a control unit for adjusting the amplification factor of the at least one transmission signal amplifier.
In order to take into account the regulations regarding the transmission power of a mobile communications device in a cell of a base station, the control unit of the compensator is configured to set a predetermined minimum amplification factor if the detected antenna signal power is less than a prespecified threshold value. This is to ensure that when the mobile communications device is near the base station, it actually transmits via an antenna usually located on the outside of the vehicle using only transmission signals in an order of magnitude which corresponds to that of the transmission level transmitted from the base station to the mobile communications device, and does not exceed this level.
Also, the control unit is configured to reduce the amplification factor in such a manner that the amplification factor is reduced to a value at which the transmission signal power of the compensator is maximised to and does not exceed a prespecified maximum value when the detected transmission signal power should exceed a prespecified maximum value.
An antenna arrangement comparable in this respect, and a regulating mechanism which is likewise comparable in this respect, have also become known from DE 10 2013 207 898 A1.
According to this prior publication, a circuit arrangement for compensating for signal attenuation during the transmission of transmission signals of a mobile communications device (via the aforementioned circuit arrangement and an antenna which is usually mounted on the outside of a motor vehicle) comprises a detector arrangement which is designed to detect whether a detected input signal level of the compensator reaches or exceeds a prespecified upper value, and whether the detected (amplified) input signal level of the compensator drops to or drops below a prespecified lower value.
If the upper value for the accordingly detected input signal level of the compensator is reached or exceeded, the adjusting apparatus should be prompted to reduce the signal level amplification generated by the signal level amplifying apparatus. Likewise, the detector arrangement should be designed in such a manner that the adjusting apparatus is prompted to likewise reduce the signal amplification generated by the signal level amplifying apparatus if the lower value is reached or passed.
For example, if the mentioned signal level amplifying apparatus comprises a signal amplifier which cooperates with an attenuation apparatus, the amplification or the attenuation can be adjusted via the attenuation apparatus. In this case, when the upper value is reached or exceeded, or when the lower value is reached or passed, the signal attenuation produced by the attenuation apparatus would be increased to ultimately reduce the signal amplification overall.
Non-limiting embodiments herein accordingly to provide an improved circuit arrangement for compensating for signal attenuation during the transmission of signals from or to a mobile communications device, and an improved method for this purpose.
In the context of example non-limiting embodiments, several surprising advantages are produced.
While in known solutions according to the prior art, the detection sensitivity of the detection apparatus is relatively high, or even as large as possible (so that even the lowest transmission signal level of the mobile communications device can be detected immediately), the example non-limiting technology herein proposes preferably reducing this detection sensitivity—that is, to shift it to higher levels. The consequence of this approach is that transmission signals of the mobile communications device are detected only after exceeding a higher level or threshold value, and the circuit arrangement is only ready to provide a corresponding amplification—that is, to amplify the transmission signal of the mobile communications device according to the control mechanism—from this transmission signal detection level and above. This initially provides the advantage that less energy is needed because the amplification control is only implemented at a later point in time.
Furthermore, this achieves the essential advantage that—in particular at very low signal levels (in particular, transmission signal levels) below the transmission signal generation level—no amplification is performed which would be too strong in some circumstances—i.e. an overcompensation—as a result of potential erroneous values. In other words, it is always ensured that, particularly when a mobile communications device is positioned close to a base station, the low transmission level set by the mobile communications device in coordination with the base station is always maintained, and the signal attenuation prespecified by the circuit arrangement is always attenuated in this prespecified attenuation—but in any case is not improperly amplified in an impermissible manner.
As long as the detected input signal and/or the detected input signal level of the compensator is below a detection level or below a lower trigger level, no transmission and amplification path is offered via the circuit arrangement (apart from parasitic crossovers), such that the communication between the mobile communications device and the base station is conducted through the vehicle body shell (which has finite attenuation).
Another important advantage is that, in the context of example non-limiting embodiments, whenever a detected input signal level of the compensator drops below a lower, prespecifiable level threshold (which is termed the transmission signal detection level and is preferably significantly higher than the lowest transmission level of a mobile communications device), preferably no amplification of the signal level is initiated. Rather, in contrast, the mobile communications device is not requested to implement an amplification in this case. Preferably, an attenuation is even provided in this case.
Because of the shift in the detection sensitivity towards higher levels, as preferably provided as part of the example non-limiting embodiments (which ultimately reduces the detection sensitivity compared to the prior art), and because of the modified amplification circuit preferably additionally provided as part of the example non-limiting implementations, in which the circuit arrangement preferably provides an attenuation rather than any amplification after the detection of the transmission band of the mobile communications device (after the signal level adjusted according to the detection sensitivity has been exceeded), not only is energy saved, but in addition, compared to conventional solutions there is much more certainty that, when the mobile communications device is in a position close to the base station, the mobile communications device transmits at the low transmission power, the value of which is specified by the base station. If the value of the mobile communications device is too low due to the attenuation, it can receive an instruction from the base station to set a correspondingly higher set value for the transmission level. Raising the detection threshold offers a number of additional advantages, namely:                achieving a lower sensitivity to mobile communications devices which are not placed in a coupling holder located in a motor vehicle, by way of example;        the aforementioned lower detection sensitivity, with the detection threshold raised, also leads to a desirable lower sensitivity to Bluetooth and WLAN signals;        in addition, an unintended response to transmission signals of further mobile telephones which are coupled into the circuit via the vehicle antenna is prevented by the low sensitivity of the selective detectors;        the reduction in system sensitivity can also make it possible for only the direct path between the mobile communications device and the base station to be active near the base station. In other words, the transmission power of a mobile communications device close to a base station is not sufficient to reach the detection threshold of the circuit arrangement (that is, the compensator) which is elevated according to example non-limiting embodiments;        in addition, the lower detection sensitivity of the detector apparatuses makes it possible to dispense with amplifiers and/or amplifier powers and filters, thereby reducing the overall assembly complexity;        significant advantages arise in terms of the insulation between the various circuit groups of the circuit arrangement; the sensitivity of the detector paths according to the prior art results in a variety of problems, since the dynamics to be processed on the circuit board can amount to approximately 90 dB—for example, in the case of LTE circuit arrangements (compensators); this can lead to almost unsolvable problems with regard to the required insulation of the various circuit groups from each other. Specifically, in the context of example non-limiting embodiments, it has been shown that particularly high blocking levels at the vehicle antenna due to third-party mobile phones or other communications modules on the same antenna can lead to a response of the detector paths, thereby significantly limiting the functionality of the circuit arrangement—that is, the compensator.        
In this case, the amplification provided as part of example non-limiting embodiments is preferably equipped with a low-pass response after the triggering threshold of the detection sensitivity is exceeded (i.e. when the higher signal level is exceeded), in order to prevent the two controls—namely the control prespecified by the compensator and the control prespecified by the network operator via the base station—from being triggered.
The solution according to example non-limiting embodiments further ensures that—due to the amplifier power being switched on and off (which occurs immediately when a lower threshold or detection level is passed, as described in DE 10 2013 207 898 A1, for example)—it is not possible for a so-called “ping-pong” effect to arise. This will be explained below.
If, for example, a vehicle is far away from a base station, then the mobile communications device receives the instruction from the base station to transmit at a comparably high signal level. Accordingly, the circuit arrangement is switched into and operated in a corresponding circuit mode for compensating for the transmission signal. The total attenuation loss which arises due to the coupling attenuation between the mobile communications device and receiver of the compensation circuit apparatus, and due to the transmission path in the circuit itself, is usually compensated for by a corresponding communication between the base station and the mobile communications device since the mobile communications device receives corresponding instructions to transmit at a transmission power which is sufficiently high that, taking into account the amplifier circuit, the mobile communications device ultimately emits via the vehicle antenna at the transmission power desired by the base station.
If the vehicle then moves closer to the base station, the transmission level of the transmission signal emitted by the mobile communications device is increasingly down-regulated with increasing proximity to the base station (due to the corresponding instruction from the base station), the amplifying apparatus of the compensator ultimately turning off the amplification abruptly when the corresponding detector sensitivity—generally the prespecified lower detection level—is reached. As a result, the transmission level of the transmission signal transmitted via the vehicle antenna is abruptly reduced, the level reduction which results being abruptly recognisable by the base station as well.
Therefore, the base station in this case will also abruptly transmit the information to the mobile communications device to quickly elevate the transmission level. As a result, a situation like that described for the starting point is reached, as if the mobile communications device is at a greater distance from the base station and the power of the transmission signal is additionally elevated via the amplifier. This accordingly leads to the undesired “Ping-pong” effect.
The “ping-pong” effect described here must absolutely be prevented for reasons of network stability. This is also reliably ensured by example non-limiting embodiments.